CVE-2026-55785 free5GC AUSF uses non-constant-time authentication comparisons and logs XRES* in 5G-AKA
Attackers with log access can read sensitive authentication material, and timing side-channels may theoretically aid bypassing 5G-AKA authentication checks.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-55785?
CVE-2026-55785 is a low-severity vulnerability in free5gc, published on 28 Aug 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official description
free5GC is an open-source implementation of the 5G core network. Prior to 1.4.5, the AUSF component performs cryptographic authentication comparisons in internal/sbi/processor/ue_authentication.go with ordinary equality helpers. Auth5gAkaComfirmRequestProcedure compares RES* and XRES* with strings.EqualFold and logs the expected XRES* value at INFO level before comparison. EapAuthComfirmRequestProcedure compares AT_MAC and XMAC with bytes.Equal and evaluates XRES == RES with ordinary string equality. These comparisons can return at mismatch-dependent times, although testing did not demonstrate a practical remote timing oracle because of HTTP/SBI timing noise. The INFO log exposes authentication material to operators, log collectors, sidecars, or processes able to read AUSF logs. This issue is fixed in version 1.4.5.
Which versions are affected by CVE-2026-55785?
3 open source packages ship an affected version, including github.com/free5gc/ausf.
| Package | Affected | Fixed in |
|---|---|---|
github.com/free5gc/ausf Go | All versions | 1.4.5 |
github.com/free5gc/ausf Go | All versions | 1.4.5 |
github.com/free5gc/ausf Go | All versions | 1.4.5 |
How do I fix CVE-2026-55785?
Upgrade github.com/free5gc/ausf to 1.4.5 or later.
Is CVE-2026-55785 being exploited?
There is no known exploitation of CVE-2026-55785 in the wild and no public exploit code.
Sources
Also known as GHSA-fp46-6vfw-gc9c, GO-2026-6328.